Fuze explosive ordance disposal circuit

ABSTRACT

The present invention comprises an electronic Explosive Ordnance Disposal (EOD) circuit which is desirably used with fuzed explosive weapons, such as projectiles having a nominal mission time. After expiration of the mission time, if the explosive has not detonated, the inventive circuit controls the energy supplied to the fuze detonation circuit to a level that is less than a threshold level required by the fuze for detonation, thereby preventing subsequent detonation of the explosive.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0001] The U.S. Government has a paid-up license in this invention andthe right in limited circumstances to require the patent owner tolicense others on reasonable terms as provided for by the terms ofcontract number DAAA21-92-C-0075 awarded by the Army.

BACKGROUND OF THE INVENTION

[0002] This invention relates generally to fuze devices which render afuze safe to handle, and more particularly to a circuit for preventingdetonation of an explosive after a predetermined period of time haslapsed, such as a thirty minute time period. In a preferred embodiment,the circuit comprises a fuze Explosive Ordnance Disposal (EOD) circuit.

[0003] The use of explosive weapons and fuzes are known in the art. Onoccasion, explosive devices fail to detonate at the appropriate time.Such munitions are referred to as duds, and are often very dangerousbecause the device may remain armed and therefore capable of high orderdetonation for an indefinite period of time. Duds typically present adanger to friendly personnel subsequently operating in the field,battlefield cleanup crews and even civilians long after a time ofconflict.

[0004] When an explosive device has failed to detonate within apredetermined mission time, or the period of time within which properdetonation can be expected, it is desirable to render the fuze safe toprevent subsequent detonation.

[0005] Prior art methods of accomplishing sterilization of a fuze havetypically used mechanical means of interrupting the battery power. Forexample, the M762/M767 fuzes utilize a mechanical spin switch thatcloses the battery circuit only while the fuze is experiencing a spinforce.

[0006] Mechanical devices can have limited reliability and higherfailure rates when compared to electronic devices that perform similarfunctions. Interacting mechanical components can wear, corrode and evenseize over time. Devices with moving parts may also have difficultywithstanding the high shock levels associated with the normal operatingenvironment of explosives devices, particularly with respect toartillery and other projectile weapons.

[0007] Some fuzes with electrically initiated explosive trains, such asthe XM773 fuze, simply use a resistor to dissipate the firing energy andany remaining battery energy to below a safe voltage or energy level.

[0008] However, for many present fuzes, which are designed to be used ina variety of applications, a simple resistor dissipation circuit is notpractical. Multi-option fuzes, such as the M782 MOFA fuze, have multipleoperating modes and are designed to satisfy a wide range of currentrequirements. As such, a resistor dissipation circuit is not alwayssufficient to reliably dissipate the energy from both the firingcapacitor and the battery within the desired time frame, which is oftenthirty minutes.

[0009] Therefore, it would be desirable to provide a device forelectronically preventing detonation of an explosive that failed toproperly detonate within a predetermined mission time. Desirably, thedevice will reliably function with all operating modes and for allapplications of a multi-option fuze. Further, it would be desirable toproduce such a device using common components that are available at arelatively low cost.

[0010] Without limiting the scope of the invention a brief summary ofsome of the claimed embodiments of the invention is set forth below.Additional details of the summarized embodiments of the invention and/oradditional embodiments of the invention may be found in the DetailedDescription of the Invention below.

[0011] A brief abstract of the technical disclosure in the specificationis provided as well only for the purposes of complying with 37 C.F.R.1.72. The abstract is not intended to be used for interpreting the scopeof the claims.

[0012] All U.S. patents and applications and all other publisheddocuments mentioned anywhere in this application are incorporated hereinby reference in their entirety.

BRIEF SUMMARY OF THE INVENTION

[0013] The presently claimed invention prevents detonation of anexplosive after a given time lapse by reducing the energy supplied tothe fuze to a value below a no-fire threshold that is required for fuzedetonation. In some cases, the power source is completely isolated fromthe firing circuit.

[0014] In one embodiment, the invention is directed to an explosiveordnance disposal circuit used in conjunction with a fuze of anexplosive. The circuit includes an electronic timer, a trigger and anoutput circuit providing an output voltage to the fuze.

[0015] After the electronic timer has lapsed, the trigger is initiatedand output voltage provided to the output circuit is controlled to alevel lower than the threshold required for fuze operation.

[0016] In another embodiment, the invention is directed to an apparatusfor dissipating the firing energy of a fuze. The apparatus includes apower source, an electronic timer, a fuze output having an outputvoltage, a trigger and a no-fire threshold circuit. After the electronictimer has lapsed, the trigger is initiated and the no-fire thresholdcircuit is activated to reduce the output voltage of the fuze outputbelow a threshold voltage required for the fuze to fire.

[0017] Other embodiments may further include a second trigger that maybe initiated after the first trigger. The second trigger desirablycauses the power source to become isolated from the fuze or the outputto the fuze.

[0018] These and other embodiments which characterize the invention arepointed out with particularity in the claims annexed hereto and forminga part hereof. However, for a better understanding of the invention, itsadvantages and objectives obtained by its use, reference should be madeto the drawings which form a further part hereof and the accompanyingdescriptive matter, in which there is illustrated and describedembodiments of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0019] A detailed description of the invention is hereafter describedwith specific reference being made to the drawings.

[0020]FIG. 1 is an electrical schematic diagram of an embodiment of theinventive Explosive Ordnance Disposal circuit.

[0021]FIG. 2 is a view of an embodiment of the inventive ExplosiveOrdnance Disposal circuit on a printed wire board.

DETAILED DESCRIPTION OF THE INVENTION

[0022] While this invention may be embodied in many different forms,there are described in detail herein specific preferred embodiments ofthe invention. This description is an exemplification of the principlesof the invention and is not intended to limit the invention to theparticular embodiments illustrated.

[0023] For the purposes of this disclosure, like reference numerals inthe figures shall refer to like features unless otherwise indicated.

[0024] With reference to FIG. 1, an embodiment of the present inventivecircuit 10 is depicted in schematic form. This embodiment isparticularly useful with fuzes such as the M782 Multi-Option Fuze forArtillery. The components of this specific embodiment have been designedfor use with projectile weapons, such as 105 mm and 155 mm howitzermunitions which typically have a 199 second mission time. A person ofordinary skill in the art will recognize that specific tolerances ofvarious components may be adjusted for use in other applications, andthat certain illustrated components may be substituted by othercomponents that equivalently produce the desired results.

[0025] The detonation of projectile weapons are typically controlled bya fuze which operates in a safe mode until arming, whereinafterdetonation may occur. Current artillery fuzes use the detection of twounique environments to activate a reserve battery and then a mechanicalsafe and arming (S&A) device to move the detonator in-line with thefiring circuit after a safe separation distance has been achieved. Thearming event is then electronically determined by the operating mode ofthe fuze. For example, if the fuze is in the TIME mode it will arm afteran operator selected time minus 0.5 seconds and then detonate at theselected time. This operation is well known in the art.

[0026] The present EOD circuit 10 may be installed in-line with thebattery that supplies the entire fuze with power. The EOD circuit 10 isdesirably configured to be initiated upon activation of the fuze'sreserve battery.

[0027] Fuzes such as the M782 typically have an operational voltagerange from 5.6 to 12 volts. The EOD circuit 10 of FIG. 1 is designed tooperate at a nominal 8 volts, but is capable of proper operationthroughout the typical voltage ranges and fluctuations encountered.

[0028] The EOD circuit 10 includes a power source input 14, a timer 22,a first trigger 26, a second trigger 28, a no-fire threshold circuit 30and a fuze input power line 18. Upon activation of the fuze's reservebattery, a full operating voltage is supplied to the power source input14, and the EOD circuit is initiated. This activates the timer 22, andalso provides a full operating voltage to the fuze input power line 18,allowing the projectile to achieve high-order detonation during themission time.

[0029] If the fuze properly detonates within the mission time, theprojectile and fuze have accomplished the mission and the EOD circuit isnot required. The EOD circuit is destroyed in the high-order detonation.However, if the fuze has failed to detonate after the mission time haslapsed, the EOD circuit works to control the energy provided to the fuzeinput power line 18 to a level lower than a threshold value required forfuze detonation.

[0030] At EOD circuit 10 initiation, operational voltage, such as anominal 8 volts DC reaches the fuze input power line 18 and the timer22. The operational voltage does not travel to the first trigger 26 orthrough the no-fire threshold circuit 30 immediately upon circuitinitiation.

[0031] The timer 22 comprises Resistance-Capacitance circuitry and an ICcomparator 36. In the embodiment of FIG. 1, the comparator 36 is a TinyCMOS Comparator with Rail-to-Rail Input model LMC7211B from NationalSemiconductor Corporation. The comparator 36 has a reference voltageline 38, an input signal line 40 and the timer output 42. When the timeris initiated, operational voltage is supplied to the reference voltageline 38, but voltage on the input signal line 40 remains low due to adrain by timer capacitors 44. As the timer capacitors 44 charge, voltageon the input signal line 40 increases. When the voltage on the inputsignal line 40 becomes equal to or exceeds the voltage of the referencevoltage line 38, the comparator 36 provides an output voltage to thetimer output 42.

[0032] The amount of time passage that occurs between initiation of theEOD circuit 10 and when voltage is provided to the timer output 42 isdesirably slightly longer than the mission time of the explosive. For atypical 155 mm howitzer artillery shell, the mission time is set at 199seconds. Therefore, the capacitors 44 of the RC circuit illustrated inthe timer 22 of FIG. 1 will reach a voltage equal to the voltage on thereference voltage line 38 approximately 200 seconds after EOD circuitinitiation. For applications where lesser or greater time spans aredesired, the capacitor and/or resistor values within the timer 22 may beadjusted accordingly.

[0033] Current from the timer output 42 allows filter capacitor 48 tocharge. As the filter capacitor 48 charges, the voltage level rises and,after reaching a threshold value, forward biases the gate of a fieldeffect transistor 32. In the embodiment of FIG. 1, the field effecttransistor 32 is a MOSFET model SI2302N manufactured by SiliconixCorporation, having a gate-threshold voltage in the range of 0.65 to 1.2volts. When the field effect transistor 32 turns on, operational voltagefrom the power source input 14 reaches and initiates the first trigger26.

[0034] When the first trigger 26 is initiated, the no-fire thresholdcircuit 30 becomes activated. In the embodiment of FIG. 1, the firsttrigger 26 is desirably a fast acting low current fuse connected toground. As depicted, the first trigger 26 is a Very Fast-Acting ChipFuse model C1Q250 from Bel Fuse Corporation, rated at 250 mA. Upon firsttrigger 26 initiation, meaning in this embodiment that current in excessof 250 mA starts to flow through the first trigger 26 and causes it toblow, current flow is diverted from ground to the base of the transistor54, which turns on the transistor 54, thereby activating the no-firethreshold circuit 30. Thus, the first trigger 26 acts as a non-volatilememory device permanently activating transistor 54. The first trigger 26desirably initiates in a very short time period. While the Bel FuseC1Q250 will open the circuit at a current of 250 mA or more, if thecurrent exceeds 750 mA, which is three times its rating, it will openthe circuit within 200 milliseconds.

[0035] The no-fire threshold circuit 30 includes a transistor 54 whichacts as a switch to connect the fuze input power line 18 to ground. Whenthe first trigger 26 is initiated, power is routed to the base of thetransistor 54. In the embodiment of FIG. 1, the transistor 54 isdesirably a high current NPN transistor, such as a model FZT849 fromZetex Semiconductors. When power is supplied to the base of thetransistor 54, the fuze input power line 18 becomes connected to groundthrough the transistor 54, thereby initiating the second trigger 28 andlowering the energy available to the fuze input power line 18 to a levelbelow a threshold energy level required by the fuze for detonation.

[0036] Due to the capacitance of the fuze firing capacitor circuitry andthe EOD circuit 10 as depicted in FIG. 1, the voltage provided to thefuze input power line 18 must be less than 1.02 volts in order to havethe total energy available to the fuze input power line 18 be less thanthe government specified no-fire threshold energy required for an M782fuze to detonate. The 1.02 volt level is determined from the specifiedno-fire energy threshold using the well known formula ½CV² and thespecific firing capacitor value of the fuze. With the specified voltageof 1.02 and a capacitance of 47 microfarads, the energy threshold is24.45 microjoules for the circuit of FIG. 1.

[0037] The second trigger 28 is desirably a second fast acting lowcurrent fuse. As depicted in FIG. 1, the second trigger 28 is a VeryFast-Acting Chip Fuse model C1Q750 from Bel Fuse Corporation. The secondtrigger 28 has a higher initiation current requirement than that of thefirst trigger 26, 750 mA with the C1Q750 fuse used in the circuit ofFIG. 1. This insures that the first trigger 26 will always initiatefirst and activate transistor 54. Typically, when the fuze input powerline 18 is grounded through the transistor 54, the second trigger 28will initiate, thereby opening the circuit and isolating the fuze andits EOD circuit 10 from the power source.

[0038] The second trigger 28 must allow appropriate current flow to thecircuit for operation of the fuze circuit and its EOD circuit comprisedof the timer 22, field effect transistor 32, first trigger 26 andno-fire threshold circuit 30, but should also be capable of isolatingthe power source when it is required to lower the fuze input power line18 below the no-fire threshold voltage. The fuze operating current canbe over 300 mA in some operating modes.

[0039] On occasion, batteries used as a power source for fuze circuitslose voltage over the mission time. In the EOD circuit of FIG. 1, thesecond trigger 28 will initiate (meaning that the fuse 28 will blow,isolating the fuze circuit from the power source input 14) if the powersource is still providing operational voltage when the no-fire thresholdcircuit 30 is activated. However, if the power source is operating at avoltage level lower than required for second trigger 28 initiation, thesecond trigger 28 will not initiate. In such a case of lowered inputvoltage, the grounding of the fuze input power line 18 through thetransistor 54 serves to lower the fuze input power line 18 energy belowthe no-fire threshold (i.e. voltage at the fuze input power line 18below 1.02 v). Specifically, in the embodiment of FIG. 1, the ZetexSemiconductors model FZT849 transistor has a collector to emittervoltage of 0.1 and will therefore lower the fuze input power line 18voltage accordingly.

[0040] Thus, the second trigger 28 should be designed to allow adequatecurrent flow to the fuze and its EOD circuit 10 during the mission time,and also to trigger isolation of the power source after activation ofthe no-fire threshold circuit 30 if it is required to lower the energyavailable to the fuze input power line 18 to a level below the no-firethreshold.

[0041] Circuit 10 also includes a first bleed resistor 56 arranged fromthe power source input 14 to ground, and a second bleed resistor 58arranged across the field effect transistor 32. In the embodimentdepicted in FIG. 1, both the first bleed resistor 56 and the secondbleed resistor 58 are 2K ohm resistors. A leakage resistor 50, desirablyan 11 megaohm resistor, is used to prevent charge build-up on the filtercapacitor 48 which could prematurely activate the no-fire thresholdcircuit 30.

[0042]FIG. 2 depicts the embodiment of FIG. 1 of the EOD circuit 10 on aprinted wire board.

[0043] The above disclosure is intended to be illustrative and notexhaustive. This description will suggest many variations andalternatives to one of ordinary skill in this art. All thesealternatives and variations are intended to be included within the scopeof the claims where the term “comprising” means “including, but notlimited to”. Those familiar with the art may recognize other equivalentsto the specific embodiments described herein which equivalents are alsointended to be encompassed by the claims.

[0044] Further, the particular features presented in the dependentclaims can be combined with each other in other manners within the scopeof the invention such that the invention should be recognized as alsospecifically directed to other embodiments having any other possiblecombination of the features of the dependent claims. For instance, forpurposes of claim publication, any dependent claim which follows shouldbe taken as alternatively written in a multiple dependent form from allprior claims which possess all antecedents referenced in such dependentclaim if such multiple dependent format is an accepted format within thejurisdiction (e.g. each claim depending directly from claim 1 should bealternatively taken as depending from all previous claims). Injurisdictions where multiple dependent claim formats are restricted, thefollowing dependent claims should each be also taken as alternativelywritten in each singly dependent claim format which creates a dependencyfrom a prior antecedent-possessing claim other than the specific claimlisted in such dependent claim below.

[0045] This completes the description of the preferred and alternateembodiments of the invention. Those skilled in the art may recognizeother equivalents to the specific embodiment described herein whichequivalents are intended to be encompassed by the claims attachedhereto.

1. An explosive ordnance disposal circuit used in conjunction with afuze comprising: a timer; a trigger; and an output circuit providingvoltage to a fuze input power line; wherein after a predetermined time,said trigger is initiated and the fuze output voltage is controlled to alevel lower than a predetermined threshold required for fuze detonation.2. The circuit of claim 1, wherein upon initiation of said trigger, aground connection is provided to said fuze input power line.
 3. Thecircuit of claim 1, wherein said trigger comprises a fuse.
 4. Thecircuit of claim 3, wherein the trigger is initiated when the fuse blowswhen the current therethrough is 250 milliamps or more.
 5. The circuitof claim 4, wherein the fuse will blow within 200 milliseconds when thecurrent therethrough is 3 times the 250 milliamps rating or more.
 6. Thecircuit of claim 1, wherein the output circuit further comprises anelectronic switch arranged to influence said fuze output, wherein uponinitiation of said trigger, said electronic switch is activated.
 7. Thecircuit of claim 6, wherein said electronic switch comprises a powertransistor having a base terminal, wherein when said trigger isinitiated, voltage is supplied to said base terminal.
 8. The circuit ofclaim 6, further comprising a second trigger.
 9. The circuit of claim 8,wherein when said electronic switch is activated, said secondary triggeris initiated.
 10. The circuit of claim 9, further comprising a powersource, wherein when said secondary trigger is initiated, said powersource is isolated from the output.
 11. The circuit of claim 8, whereinsaid second trigger comprises a fuse.
 12. The circuit of claim 11,wherein the second trigger initiates by blowing when the currenttherethrough is 750 milliamps or more.
 13. The circuit of claim 12,wherein the second trigger will blow within 200 milliseconds when thecurrent therethrough is 3 time the 750 milliamps rating or more.
 14. Thecircuit of claim 1 wherein the timer is comprised of a timer circuitconstructed and arranged to take a predetermined time to initiate thefirst trigger.
 15. The circuit of claim 14 where the timer circuit iscomprised of a comparator having a reference voltage line and an inputvoltage line, the input voltage line being connected to a capacitorelement which takes a predetermined time to charge sufficient toequalize the voltage on both the reference voltage line and the inputvoltage line, thereby providing the comparator with an output voltage.16. The circuit of claim 15 wherein the predetermined time to charge thecapacitor element is at least 200 seconds.
 17. The circuit of claim 1wherein the predetermined fuze threshold output voltage is 1.02 volts.18. An apparatus for dissipating the firing energy of a fuze comprising:a power source; a timer; a fuze power input; a trigger; and a no-firethreshold circuit; wherein after a predetermined time, said trigger isinitiated and said no-fire threshold circuit is activated to reduce theoutput voltage of said fuze output below a predetermined thresholdrequired for a fuze to fire.
 19. The apparatus of claim 18, furthercomprising a second trigger, wherein when said no-fire threshold circuitis activated, said second trigger is initiated.
 20. The apparatus ofclaim 19, wherein when said second trigger is initiated, said powersource is isolated from said fuze output.
 21. The apparatus of claim 18,further comprising a second trigger connected to a power supply, thesecond trigger being initiated when the current flowing through thesecond trigger exceeds a predetermined current threshold, therebyisolating the EOD circuit from the power source.
 22. The apparatus ofclaim 21, wherein when said second trigger is initiated, said powersource is isolated from said fuze output.
 23. The apparatus of claim 18,further comprising a second trigger, wherein when said no-fire thresholdcircuit is activated and said power source is supplying a lower voltagethan said threshold voltage required for a fuze to fire, said secondtrigger is not initiated.
 24. A projectile including a fuze and areserve battery which is activated after first and second environmentconditions are verified, the projectile including an ordnance disposalcircuit (EOD) comprising: a power source, power being supplied to theEOD circuit upon activation of the reserve battery; a timing circuitwhich is activated when power is supplied to the EOD circuit; a triggerelement which is triggered by the timing circuit after a predeterminedtime, and and a fuze output voltage control circuit connected to thetrigger element, which is constructed and arranged to pull the fuzeoutput voltage below a predetermined no-fire threshold voltage valueupon triggering of the trigger element whereby the fuze is incapable ofdetonating the projectile.
 25. The projectile of claim 24 wherein thepower source is a battery supplying a voltage in the range of 5.6 to 12volts.
 26. The projectile of claim 24 wherein the timer circuit iscomprised of a comparator having a reference voltage line and an inputvoltage line, the input voltage line being connected to a capacitorelement which begins to charge upon activation of the timing circuit,the predetermined time to trigger being the time sufficient to chargethe capacitor element to equalize the voltage on both the referencevoltage line and the input voltage line, thereby providing thecomparator with a comparator output voltage connected to the fuze outputvoltage control circuit.
 27. The projectile of claim 26 wherein theoutput voltage control circuit includes an FET transistor connected to aFET activation capacitor which is charged by the comparator after thepredetermined time has elapsed, the FET transistor being turned on whenthe FET activation capacitor has charged sufficiently to exceed the gatethreshold voltage of the FET transistor.
 28. The projectile of claim 27wherein the trigger element is a first fuse which blows when the FETtransistor turns on and the current flowing through the fuse exceeds afirst predetermined current threshold, the first fuse blowing activatingthe fuze output voltage control circuit to pull the fuze output voltagebelow the predetermined no-fire threshold voltage value.
 29. Theprojectile of claim 28 wherein the fuze output voltage control circuitincludes a transistor connecting the fuze output to ground, thetransistor being turned on when the first fuse blows, thereby pullingthe fuze output voltage below the predetermined no-fire thresholdvoltage value.
 30. The projectile of claim 29 wherein the fuze output isalso connected to a second fuse, which is connected to the power source,the second fuse blowing when the current flowing through the second fuseexceeds a second predetermined current threshold, thereby isolating theEOD circuit from the power source.
 31. A method for disposing ofordnance which fails to detonate within a predetermined mission timecomprising the steps of: providing a projectile including a fuze andreserve battery which is activated after first and second environmentconditions are verified, the projectile including an ordnance disposalcircuit (EOD) comprising a power source, a timing circuit, a triggerelement and a fuze output voltage control circuit; starting the timingcircuit upon activation of the reserve battery; triggering the triggerelement after the timing circuit has operated for the predeterminedmission time; pulling the fuze output voltage supplied by the fuzeoutput voltage control circuit below a predetermined no-fire thresholdvoltage upon triggering of the trigger element.
 32. An explosiveordnance disposal circuit used in conjunction with a fuze comprising: atimer; a trigger; and an output circuit connected to a fuze input powerline; wherein after a predetermined time, said trigger is initiated andthe energy at the fuze input power line is controlled to an energy levellower than a predetermined threshold energy required for fuze operation.33. The explosive ordnance disposal circuit of claim 32 wherein theenergy level is 24.45 microjoules.